Vacuum flotation device

ABSTRACT

A vacuum foam flotation apparatus for treatment of turbid liquids in which the liquids flow in a trough in an evacuated housing, while conveying means move laterally of the trough and displace foam from the surface of the liquid in the trough into foam pockets arranged along the side of the trough. At least the first portion of the trough has laminar liquid flow therein, while agitating means may be provided to agitate the liquid in the trough beyond the region of laminar flow.

United States Patent Gotte 4 1451 Dec. 12, 1972 [s41 VACUUM FLOTATION DEVICE 3,479,281 11/1969 Kikindai ..210/221 x l l. m1 Inventor August we, .Ronhmder wmket 3,133,313 311323 32.50??? 513133;?

23, Aachen, Germany [22] Filed; Nov. 9 1970 Primary Examiner-John Adee Attorney-Walter Becker [21] Appl. No.: 87,879 i y [57] ABSTRACT [30] Foreign Application Priority Data A vacuum foam flotation apparatus for treatment of turbid liquids in which the liquids flow in a trough in Nov. 11,1929 Germany ..P 19 56 530.] an evacuated housing, while conveying means move Aug. 11, I? 9 Germany 20 39 871.4 7 laterally of the trough and displace foam from the face of the liquid in the trough'into foam pockets-ar- [52] US. Cl ..210/221, 210/322 Tanged along the side of the trough At least the first [51] Int. Cl. ..B0ld 21/24 portion of the trough has laminar liquid flow therein, of Search V agitating means may be provided to agitate the liquid in the trough beyond the region of laminar flow. [56] References Cited v 19 Claims, 14 Drawing Figures UNITED STATES PATENTS V 1,176,428 3/1916 Callow ..210/221X PATENTEB DEC 12 m2 sum 2 OF 5 FIG. 2

INVENTOR Jaw/v g BY FIG 3 PATENTED DEC 12 I973 3 705,650

SHEET 3 OF 6 FIG. 4

FIG. 5

INVENTOR /(/s/ 615/92 BY Q 1 VACUUMFLOTATION DEVICE The present invention relates to a flotation device for t practicing the well-known vacuum flotation method according to which the gases, especially air, dissolved in the turbid water, are by means of underpressure separated in a very fine distribution so that said gases in statu nascendi collect at the surfaces of the solid ingredients which in a manner known per se have been demoistened by flotation re-agents and cause the same to float upwardly.

Although it has been known that the vacuum flotation operates without time loss over the flotation method under atmospheric conditions, because in this instance it is not the point to cause prevailing air bubbles to adhere to the surfaces of solid materials, because the air dissolved in water will in a vacuum preferably separate on the surfaces of. solid material in the form of fine bubbles, researcheshave heretofore been unsuccessful to build a flotation device which will permit exploiting the advantages *inherent to the vacuum method. l

The heretofore known vacuum flotation cells have been designed as relatively deep containers of a conical or cylindrical shape in order to assure a sufficient staying time of the turbid substance in the cell.

Thus, for instance, the original Elmore vacuum flotation cell described in the handbook, Erzund Steinkohlenaufbereitung von H. Schennen und F. Jungst, 1913, pages 333 to 336, has a conical shape with its tip pointing upwardly while the supply of the flotation turbid substance is effected centrally through the circular bottom. Consequently, the flotation foam which contains the concentrates rises toward the tip of the conical flotation while from air it is withdrawn through a barometric drop line. This Elmore cell, however, did not yield satisfactory separating results because, in view of the applied underpressure, the strong gas development in the vacuum on one hand drives considerable quantities of sediments or waste into the concentrate, and on the other hand the air bubbles adhering to the concentrate are in part again destroyed so that considerable quantities of concentrate are lost with the waste. It was intended to remedy this defect-by arranging in series a plurality of Elmore cells with the vacuum increasing from cell to cell. Aside from the considerable increase in the installation costs by the employment of Elmore cells in series instead of a single Elmore cell, no material improvement of the separating results could be realized by means of said last mentioned device. a

The drawbacks of the Elmore cell, including the Elmore cells improved in the meantime, were so great that they were unable to compete with the well-known agitating flotation cells; This fact has been verified in the German technical literature, Der deutsche Steinkohlenbergbau, Volume 4/ 1960, page 329.

From the Engineering News Record dated Feb. 25, 1943, pages 576l, a vacuum flotation cell has become known which differs from the Elmore cell primarily in that instead of a conical shape it has a. cylindrical shape. These cells were likewise unable to are connected to each other in such a way that the.

respective type of foam of a given flotation stage in one cell is conveyed to a successive stage which is located at a higher level and furnishes more valuable concentrates. The said foam type is conveyedinto a separate cell with the flow of the withdrawn gas, whereas the residue of the last working step is by force of gravity returned to the preceding working stage which is located on a lower plane. By admitting additional air, where bubbles are introduced into the flotation turbid substance in the individual flotation cells so that the separation is effected partially with the added air and partially with the air which leaves the turbid water under a vacuum.

The individual flotation cells according to the said German Auslegeschrift has the shape of a slender cone pointing with its tip in downward direction while its upper end continues in a cylindrical foam chamber and a cylindrical inlet part arranged above said foam chamber, the flotation turbid substance being conveyed tangentially to the inlet part. For withdrawing the respective foam type there is provided a cylindrical overflow container which is located in the center of the foam chamber. The waste is withdrawn at the tip of the flotation cell where also the additional air is introduced.

The above mentioned connection of a plurality of such flotation cells in order to post flotate the foam type as well as the waste, proves that with this design of the flotation cell, it is likewise necessary to employ a plurality of such devices in order to obtain satisfactory results. Tests so far have failed to prove that the above designed circuit furnishes satisfactory results. At any rate, the above heretofore known circuit requires a number of expensive devices and also requires considerable space which considerably exceeds the space required for agitating flotations.

U.S. Pat. No. 2,248,177 discloses a device for purifyingsoiled water which hasbeen saturated with air and has been withdrawn fromthe manufacturing operations involving the making of paper, cellulose and textiles, with air bubbles leaving the water in view of a reduction of pressure, said air bubbles carrying the solid particles (floc) to the surface. These soiled waters have previously been freed from heavy deposits in decanting devices. Therefore, this method. is not intended to separate solid particles in conformity with their different wettability as is the fundamental idea of the flotation method, but is concerned merely with the floating of all floatable material from the water in an endeavor to obtain pure water. Inasmuch as the soiled water does not contain any deposits, with this water purification method, no deposit can adhere between the floating substances carrying air bubbles even when during the decanting of the soiled water nonseparated material adapted to sink can be enclosed by the floating substances, it is of no consequence, but actually an advantage because the floating materials represent waste and because the codischarge of deposits with the floating substances will benefit only the intended purification of the water. With this vacuum water purification method, the difficulties occurring in the conventional vacuum foam flotation with regard to a clean separation of floating material from non-floating material will not occur. The water purification method according to U.S. Pat. No. 2,248,177 can therefore not convey to the expert in this field any solution to overcome the above mentioned difficulties.

It is, therefore, an object of the present invention to provide a vacuum flotation device which will take advantage of the above outlined advantages of the vacuum flotation method while considerably reducing the flotation period over agitation flotation and furnishing at least the same good foam types.

These and other objects and advantages of the invention will appear more clearly from the following specification, in connection with the accompanying drawings,

in which:

FIG. 1 shows a diagrammatic longitudinal section through a vacuum flotation device with the important accessories pertaining thereto.

FIG. 2 represents a horizontal section through the vacuum flotation device according to the invention,

' saidsection being taken along the line IIII of FIG. 1.

7 FIG. 3 represents a cross section through the vacuum flotation device according to the invention, said section being taken along the line IIIIII of FIG. 1.

FIG. 4 shows the vacuum flotation device with an impact screen in the turbid flow, FIG. 4 representing a horizontal section taken along the line II of FIG. 5.

FIG. 5 is a cross section through the device of FIG. 4, said section being taken along the line II-II of FIG. 4.

FIG. 6 shows a longitudinal section through the vacuum flotation device with nozzles for introducing air, water or turbid substance into the turbid flow.

FIG. 7 is a cross section of thedevice of FIG. 6, said section being taken along the line VII-VII of FIG. 6.

FIG. 8'illustrates a longitudinal section through the vacuum flotation device with an agitating mechanism.

FIG. 9 is a horizontal section of the device of FIG. 8, said section being taken along the line VIIIVIII of FIG. 9.

FIG. 10 illustrates the device of FIG. 8, but with a shorter steeply inclined trough in front of the agitating part.

FIGS. Ila to 11d respectively illustrate various methods for temporarily withdrawing the flotation turbid substance from the vacuum, ventilating the withdrawn turbid substance and subsequently re-introducing the same into the device working under a vacuum.

The invention is based on the finding of the inventor I that the shape of the heretofore known vacuum flotation cells do not do justice to the processes during the course of the vacuum flotation method, at least not to the desired extent and that only by adapting the shape of the device to the respective processes, the advantages of the vacuum flotation method can be realized to their full extent.

The vacuum flotation device according to the invention is characterized primarily in that it has the shape of a closed trough with an inlet for the flotation turbid substance at one end and a discharge therefor at the other end and with a connection to asource of vacuum above the turbid level. The vacuum flotation device according to the present invention is furthermore characterized in that the depths of the trough and thereby the level of the flotation turbid fluid passing through the trough is dimensioned only so great that the massing of the gas bubbles which under the influence of a vacuum separate from the turbid water and rise to the surface is in the vicinity of the surface of said turbid water limited to an amount with which the driving of deposits or waste into the concentrating foam will be prevented to a material extent. The trough has a suitable depth and a relatively large surface and is connected to a vacuum source while the length of the trough is so dimensioned that the time required for the turbid water to pass through approximately equals the time required for the air dissolved in the turbid water to separate therefrom and reach the surface when the vacuum is applied.

In view of the arrangement outlined above, the relative movements of the air bubbles loaded with concentrate decrease and their mutual distance increases so that also the stripping off of the concentrate grain, as it may be caused by the gas bubbles, rub against each other, will be avoided at least to a major extent.

The proper dimensioning of the depth of the trough can, with a given vacuum, easily be ascertained by tests for each desired flotation material. The shape of the trough of the flotation cell will, in contrast to the heretofore known conical or cylindrical shapes bring about a substantially laminary turbid flow in one direction. This shape of the trough will therefore permit adjusting the stay of the flotation turbid medium in a vacuum by longitudinally dimensioning the trough or adjusting the flow velocity to an optimum extent and will prevent the mixing of turbid ingredients from which the dissolved gases have already been freed to a major extent, with such turbid components which are still in the process of being separated from the gas. In this way, an optimum flotation success will be assured.

The surface, which is relatively great with regard to the depth of the flotation turbid flow will furnish a large lateral space of movement for the concentrate foam layer being formed so that on one hand an undue compacting of said concentrate foam layer will be prevented while on the other hand a too short stay of said concentrate foam layer on the turbid surface will be eliminated. In this way, deposit particles enclosed in the foam layer will have sufficient opportunity at the proper time to be separated from the foam layer.

If the supply of finely distributed additional air to the floatation turbid substance appears expedient, the trough shape of the flotation cell will permit arranging the means for feeding the additional air in conformity with the invention at that portion of the trough where the natural separation of the gases dissolved in the turbid liquid has markably been reduced. The shape of the trough thus permits an aimed additional air supply at that area of the turbid flow where it may be necessary and where it will not disturb but aid the flotation process which occurs in a, particularly effective manner, in view of the gases being discharged under vacuum.

The supply of additional air may, according to a further feature of the invention, advantageously be effected in such a way that the additional air is supplied together with water which preferably under overpressure has been saturated with air or gases. These water or turbid flows may, according to a further development of the invention, be provided with flotation reagents.

According to a further feature of the invention, the trough has a depthwhich increases in the direction of flow of fluid therethrough. As a result thereof, with naturally decreasing gas separation from the turbid water flowing in the trough, the most favorable massing of the gas bubbles in the upper turbid layers is still maintained for a longer period of time by increasing the depth of the turbid substance so that the concentrate particles which have not yet been loaded with air bubbles will have an increased possibility to move and adhere to said air bubbles and thusto float into the foam layer. It has proved advantageous in connection with the flotation of turbid substances from which many particularly courser or heavier ingredients easily separate, to design rather steeply the depth of the trough which increases in the longitudinal directionof the trough. An expedient and preferred design of the invention is characterized primarily in that the width of the trough increases in the direction of flow of the turbid substance. As a result thereof, the surface of the flotation turbid flow is widened in the direction of flow, in other words, with the progress in the flotation process, so that the foam being formed will have a better lateral extension possibility which will safely prevent an undue compacting of the foam at the surface of the turbid substance.

The depth and width of the trough will, in combination with the mentioned problems, naturally also serve for the controlof the flow velocity of the turbid substance.

For purposes of continuously withdrawing the concentrate foam, the trough-shaped vacuum flotation cell may, according to a further development of the invention be equipped at one or both longitudinal sides and within its chamber which is under a vacuum, be provided with foam pockets and may above the level of the turbid substance be provided with rotating paddles or strippers in such an arrangement that the latter will strip the foam off the surface of the flotation turbid flow and transverse thereto into the foam pockets. The foam pockets may, according to a further feature of the invention, in the longitudinal direction of the troughshaped flotation cell be subdivided into a plurality of sections separated from each other. Each of these sections is provided with a discharge pipe for discharging the foam. In this way it will be possible to withdraw from the cell different concentrates, which represents an advantage which is not obtainable by heretofore known vacuum flotation cells.

The supply of turbid substance to the trough-shaped flotation-device is, in conformity with the invention, effected through a feeding opening which widens continually and preferably assumes the width of the trough, so that in the entire trough, there will be produced a substantially whirl or turbulence-free turbid flow which does not interfere with the floating up of the concentrate particles loaded with air bubbles in the turbid flow.

In view of the above described geometric adaptation of the vacuum flotation device to the character of the vacuum flotation method, it is possible in a single trough and in flotation periods of less than seconds, especially in the foam concentrate, to obtain enrighments which correspond to the enrichments obtainable with the best commercially obtainable agitating flotation devices, or they may even exceed the same. The vacuum flotation device according to the invention thus creates the possibility for further improvements in the. discharge of the waste by postfloating. In this connection, according to the finding of the inventor, the series arrangement of a plurality of expensive vacuumflotation troughs is not necessary, but surprisingly, in most instances, it will suffice to have the vacuum flotation device followed, according to the invention, by a single conventional flotation cell working under atmospheric pressure, for instance, an agitator flotation cell. 7

When providing such second flotation stage in a conventional agitator cell, it has been found that the enrichment of the waste or discharge of the vacuum flotation cell relative to the enrichment of similar waste from the agitator flotation, is qualitatively, quantitatively, considerably better. This is assumed to be due to the fact that the turbid liquid is d-e-gasified to a major extent and, in view of the atmospheric pressure within the region of the agitator cell will easily absorb air, or the flotation under a vacuum is completed at a time at which still amaterial quantity of airis dissolved and retained in the turbid substance.

. Tests with the flotation device according to the present invention have proved that the quality of the turbid flow is of great influence on the flotation result. Thus, it-has been found that with a turbulent solid flow, the faulty discharges in the waste contain a greater proportion of coarser than of finer grain, whereas with a primary laminary turbid flow, the proportion of fine grain in the faulty discharges is predominant. This property is probably due to the fact that in a turbulent turbid flow, the coarser solid particles will, in view of strong collisions, more easily be separated again from the adhering air bubbles than is the case with the finer solid particles, whereas in a laminary turbid flow, the coarser solid particles are able unimpededly to float upwardly, whereas the finer solid particles will, in view of their linear movement corresponding to their laminary flow have no sufficient opportunity to attach themselves to air bubbles. The employment of flocculation means in order to floc the fine solid particles, has'not yielded a satisfactory result because the flocs are again destroyed to a major extent in view of the air separation suddenly occurring at the charging end of the trough.

Therefore, the problem arose to avoid the above mentioned grain enrichments in the faultymaterial of the waste as they are brought about by the property of the turbid flow, and thereby to materially improve the discharges or waste.

This object has been realized according to the present invention by providing means in the flotation device at spaced arrangement with regard to the charging end, by which means the primary laminary turbid flow is in down flow direction subjected to turbulence.

in this way, at the charging end there will be maintained a zone of laminary turbid flow which has such a length that the coarser solid components will be able to float upwardly without any major mutual collisions and that in downstream direction a turbulent flow zone will be created in which the finest particles not yet adherent to air bubbles will, in view of a vivid movement in the turbid flow have sufficient opportunity to attach themselves to air bubbles and to float upwardly. In view of this differentiated adaptation of the character of the turbid flow to the various granular sizes of the flotation material, it will be appreciated that on one-hand the sinking of coarse floating material into the waste will be made more difficult while on the other hand the upward floating of fine floating particles will be improved quantitavely. In this way, considerably purer waste discharges will be obtained.

As means for converting the laminary turbid flow into a turbulent flow there is employed an impact screen built up of rods and meshing, which impact screen is arranged transverse to the turbid flow and in spaced relationship to and below the surface of said screen. Such impact screen will impact turbulent movements upon the laminary turbid flow in downstream direction. It will, however, not affect the upper layers so that-in the upper layers the laminary flow is maintained which aids the formation of foam. Depending on the desired magnitude of the turbulence in the turbid flow, also a plurality of impact screens with the impact rods thereof offset with regard to each other may be employed. A particular advantage of the turbulence consists in that under a vacuum a greater portion of the air dissolved in the turbid water will become free than is the case in a laminary turbid flow so that generally also in the zone of turbulence located downstream, sufficient quantities of air will be available for the floating of the fine solid particles.

The turbulence in the turbid flow may, according to the invention, also be produced by a continuous or pulsating introduction of water, turbid flow, or compressed air flows into the laminafy turbid flow at any desired area thereof and transverse to the direction of flow thereof. The water or turbid flows are, according to a further feature of the invention, saturated with air or gases, preferably under an underpressure. In this way, it will at any rate be possible to make sufficient air available in the zone of turbulence in order to assure an optimum floating of the finest solid particles. The air saturated water or turbid flows are preferable to the compressed air flows because they distribute themselves faster and more uniformly over the entire turbulent portion of the turbid flow than is the case with compressed air which very quickly rises to the surface, and because the air leaving the flows under a vacuum will immediately attach itself to the dehumidified solid particles.

Flotation re-agents may, in conformity with the requirements and circumstances, be admixed to the water or turbid flows.

The laminary turbid flow may, after a certain course also be subjected to turbulence by an agitator mechanism which is arranged in the trough, preferably in a deepened portion. The agitator mechanism is, in conformity with heretofore known agitator flotation operations, equipped with horizontally rotating and upwardly feeding agitating blades and is separated from the laminary turbid flow range by a transverse wall which extends not quite to the bottom of the trough. With this design of the agitator mechanism, any disturbance of the laminary turbid flow zone is prevented by the agitator mechanism, and in the turbulent zone an upward flow is created which facilitates the upward floating of the fine flotatable particles. Moreover. floatable particles which were previously misdirected and deposited on the bottom will again be whirled up by the agitator mechanism and will thus be returned into the turbulent turbid flow where they have the opportunity of attaching themselves to air bubbles.

The mentioned arrangement of an agitator mechanism primarily corresponds to the referred to arrangement of a conventional agitator flotation. The arrangement of the agitator mechanism is,however, as far as necessary structure and space requirement is concerned materially more favorable and more effective because it works with a vacuum. The agitating mechanism unit may have any desired cross section, e.g. may be polygonal or may be round.

In many instances it has proved very effective to carry out the desired ventilation of the flotation turbid substance in such a way that after a certain movement orstroke in the trough-shaped device, or after a corresponding lapse of time, the flotation turbid substance is temporarily taken out of the vacuum range, is then ventilated and subsequently is returned into the device or its extension working under a vacuum. In this manner a particularly thorough ventilation of the turbid substance will take place which will revive the flotation.

Referring now to the drawings in detail, the flotation cell 1 has the shape of a trough and is closed in' a vacuum-tight manner by means of a cover 2. At one trough end there is provided a feeding nozzle 3 for the flotation turbid substance whereas a discharge 4 for the turbid substance is provided at the other end of said trough, said discharge 4 being adapted to be controlled by a valve 5. The feeding nozzle 3 is so shaped that it steadily widens from the cross section of its feeding pipe and eventually assumes the width of the trough. In

- this way, a substantially laminary turbid flow a is maintained in the trough. The valve 5 serves for controlling the level of the turbid flow in the trough and thereby the level of the foam layer. The bottom of the trough is inclined downwardly in the direction of flow of the turbid substance. The depth of the trough and thereby the depth of the turbid content thus increase in the direction of the flow. As will be seen from FIG. 2, the trough has sidewalls which in the direction a of the flow flare so that also its width increases in the direction of flow. Arranged on each or both longitudinal sides of the trough there are foam pockets 6, 7, 8, each of which is provided with a discharge pipe 9, 10, l1, and a control valve l2, l3, 14, respectively. Above the level of the turbid substance, each foam pocket 6, 7, 8, has associated therewith a foam stripping device, known per se, which comprises rotating paddles 15, 16, 17, the arrangement being suchthat said paddles strip off the foam in a direction transverse to the flow direction a of the flotation turbid flow and from the surface of the latter into the foam pocket.

The foam discharge lines 9, 10, 11, and the turbid discharge 4 lead into a collector 90, 100, and 40. The flotation cell and the collector or collecting container are, by means of the pipe lines 18, connected to a vacuum pump, not shown in the drawing. The supply of the flotation turbid substance is effected in a known manner through an agitator vessel 19 and a barometric riser 20 in which a control valve 21 is arranged, whereas the discharges from the collecting container 40 and the concentrates caught in the foam pockets 6, 7, 8 are withdrawn from the collecting containers 90, 100, 110 through barometric drop line 22, 23, 24, 25 or by pumps. The quantities to be withdrawn from the collecting containers are adapted to be controlled by the valves 26 -29.

' The flotation re-agents necessary for the flotation process are admixed to the flotation turbid substance in the agitating vessel 19. The re-agents may, in a manner known per se, prior thereto be heated up in vessels, not shown in the drawing, in order to improve their efficiency.

The length of the vacuum flotation trough is, with the vacuum to be applied and the flow velocity of the turbid substance, so dimensioned that'the separation of the gases dissolved in the turbid liquid and under the influence of the applied vacuum be completed to the desired extent at the exit end of the trough. The level of the turbid flow is, by correspondingly dimensioning the distance of the .trough on the basis of previous tests, so adjusted that the massing of the air bubbles in' the vicinity of the surfacewill not be'able todrive any material quantities of sinkable goods into the concentrate foam.

Near the exit end of the flotation cell, means, for instance, a porous body 30 may be provided with acompressed air connection 31 in the bottom of the trough in order to add foreign air in finely divided condition to the turbid fluid which has been degasifled to a certain extent under the influence of the vacuum. The said foreign air supplements the flotation process and, as the case may be, extends the same.

The two following tables indicate, by way of comvparison, the flotation results as obtained by a vacuum flotation device according to the invention, and by means of a heretofore known agitating cell. With the flotation devices, equal quantities of the bituminous coal mud turbid of 0.75 to millimeters granular size and approximately 21 percent ashes were charged.

Table l: Underpressure-flotation with postflotation of the discharge Component Ash Content Duration Individual Added Individual Medium of by by by by Flotation Weight Weight Weight Weight Seconds Concentrate 1 26.5 26.5 4.1 4.1 120 Concentrate 2 48.0 74.5 7.0 6.0 120 Concentrate 3 4.5 79.0 19.4 6.7 120 Mine Waste 21.0 100.0 76.9 21.5

Total 100.0 (21.5) 360 Table 2: Agitator-flotation alone By means of the vacuum flotation device according to the present invention, in the very short flotation period of only 25 seconds, a weight yield of 72 percent was realized and concentrates with a medium of 6.1

percent by weight were obtained. In contrast thereto, the agitator mechanism cell yielded a concentrate with a medium of 6.7 percent by weight of ashes and wastes with 76.9 percent by weight of ashes only after a flotation period of 360 seconds.

The non-weight outflows of the vacuum flotation device with hardly 60 percent by weight of ashes were by postflotation over a total of only seconds split up in an agitator cell into two types of I and II of middlings of 12 percent by weight and 33.3 percent by weight of ashes. In this way, in the final mine waste a content of 81.1 percent of ashes was obtained. Whether the middlings 11 may entirely or partially be added to the concentrate or has to stay in the flotation circuit has to be decided from instance to instance.

The vacuum flotation device was driven with a vacuum of approximately 700 Torr.

Similar surprisingly good results have also been obtained in connection with the flotation of mineral turbids.

The devices illustrated in FIGS. 4 l0 correspond as to their principal features to those of FIGS. 1 to 3. In other words, the devices of FIGS. 4 to 10 have a flotation cell 1 in the form'of a trough which is closed in a vacuum-tight manner by a cover 2. Furthermore, these devices have a steadily widening feeding nozzle 3 for the flotation turbid substance, which latter is free from turbulence passed into saidtrough so that there a substantially laminary flow will be maintained. At the distance x from the inlet end of the turbid substance an impact screen 32, 32' is arranged in trough 1 and transverse to the flow of the turbid substance. This impact screen is composed of one or more rows of rods and ends at the distance 1 below the surface of the turbid flow. By means of said impact screen, the laminary turbid flow has its lower portion subjected to turbulence, whereas that portion of said turbid flow whichflows over the impact screen retains its laminary character favorable to the formation of foam. The turbid flow in trough l is thus subdivided by the impact screen into a laminary zone x and downstream into a turbulent zone y. The laminary zone x is dimensioned so long that the coarser flotation material will be able to float upwardly into the foam layer, whereas the turbulent zone will be dimensioned so long that also the fine flotation material will be sufficient also to float upwardly.

The example according to FIGS. 6 and 7 has one or more outflow bodies 33 which are spaced by the distance x from the charging end (said spacing may also be very short). The said outflow bodies 33 are provided for introducing and distributing compressed air, water, or turbid flows over the entire width of the laminary flow 8 which flows in trough l. The outflow bodies may consist of porous ceramic bodies produced by sintering or as illustrated, may consist of pipes with outflow openings in their walls. The mentioned media are introduced in a continuous or pulsating way into the turbid flow transverse to the flowing direction of the latter. They impart turbulence upon the turbid flow downstream so that again in the above mentioned trough, a laminary flow zone x is formed and an adjacent turbulent zone y. The transverse flows composed of water or turbid substances are preferably under overpressure saturated with air which permits the transverse flows to flow out in the turbulent zone y under the there prevailing vacuum into the turbid flow. These transverse flows may, in conformity with the requirements, also have flotation re-agents admixed thereto in order to replace the re-agent losses in the laminary zone or, if desired, to produce changes in the flotation discharge.

The outflow bodies 33 may also be employed in connection with impact screens 32, 32' according to FIGS. 4 and 5.

According to the embodiment of FIGS. 8 and 9, the laminary turbid flow a is subjected to turbulence by an agitating mechanism 34 which rotates in trough 1. The said agitating mechanism is located in spaced arrangement from the charging end of the trough in such a way that the turbulent zone y produced by said agitating mechanism will leave a zone x of the laminary turbid flow free from turbulence, which zone 1: is sufficient to permit the coarser ingredients of the flotation material to rise into the foam layer. The intensity of the turbul'ence may precisely be adapted to the requirements by varying the speed of the agitating mechanism. Also, the cross-sectional shape of the cell may contribute to a desired degree of the turbulence because a multicorner cell brings about a stronger turbulence than, for instance, a round cell. The zone of turbulence produced by the agitating mechanism is, as illustrated in the drawing, preferably separated from the laminary flow zone by a transverse wall 35 which at the bottom of the groove has one or more passages 36 for the turbid substan'ce which flows out of the laminary zone. The partition prevents the turbulent zone y during increase in the speed of the agitating mechanism from being displaced in an undue manner into the laminary zone x. The agitating blades of the agitating mechanism 34 preferably rotate in a depressed portion 37 of the flotation device about a vertical axis 38 and have such a pitch angle that they convey the flotation turbid flow upwardly. Above the agitating blades there is provided a quieting grate 39. Below the agitating mechanism one or more feeding lines 41 for compressed air or preferably for water saturated with air under overpressure or for turbid flow with or without flotation reagent addition lead into the flotation device.

The turbulent zone y may, according to the requirements, be laterally widened relative to trough 1 as indicated in dot-dash lines in FIG. 9. Tests of comparisons have been run with Portuguese iron ore difficult to float, which was ground fine to 0.1 millimeters grain size. The discharge of the first mentioned device which works without turbulent zone had an iron ore content of from 20 to 21 percent, whereas the device working with a turbulent zone produced discharges with only 10.6 percent iron ore.

According to FIG. 10, the turbid flow to be floated enters at 101 into the trough-shaped part 102 of the device, the bottom 111 of which, is inclined at a relatively steep angle. The rising foam is drawn off by strippers 108 and is passed into the foam pockets. The tur bid flow treated in part 102 passes through the passage 103 into the agitating chamber 104 where it is agitated by the agitating mechanism 105. The here rising foam is withdrawn from the surface of the turbid substance by strippers 108.

The level of the turbid flow and thereby the height of the foam are controlled by means of an adjustable overflow pipe or overflow dam a. The discharge flows over this dam and is discharged at 106. The device furthermore comprises a connection 107 for emptying the device.

Referring now to FIGS. 11a 11d, the upper portion of FIG. 11a corresponds substantially to that of FIG. 1. The groove or trough l is subdivided by the partition 41. This partition is interrupted at its lower end at 41a, and this opening may be opened and closed selectively at any desired time by an upwardly and downwardly movable slide 42.

. The turbid substance which is supplied at 3 is within the region up to the partition 41, guided precisely in the same manner as with the device according to FIG. 1.

When the flotation turbid substance is to be ventilated therebetween, it is discharged into the container 45 whichis open toward the top and thus is connected to the atmosphere. Also, in this instance, flotation means may be added in conformity with any requirement. The supply of turbid substance to the container 45 is effected by the drop line 43 with valve 44. For purposes of withdrawing the turbid substance from the underpressure range of the trough 1, it is necessary to overcome this underpressure. This is effected in two ways, once mechanically, hydraulically, or pneumatically by establishing a suction from container 45 through line 43 to the trough, and secondly, by providing a distance H between the level of the turbid substance in groove 1 and the level of the turbid substance in container 45, which distance H has such a height that the weight of the turbid column of the height H together with the effect produced in container 45 in the described manner overcomes the underpressure.

As means for thus overcoming the underpressure prevailing in trough 1, four examples may be mentioned. According to FIG. 11a, compressed air is introduced into the conduit 46 so that an injector pump effect is produced. The design according to FIG. 11b is characterized in that the compressed air which is admitted at 47 and which enters the horizontal continuation of the downwardly extending pipe 43 will, in view of the cylindrical insert 48 in the container 45, bring about that the turbid substance is, similar to a Pachuca tank, conveyed in a vertical circular ring within the cylinder in upward direction, and outside the cylinder again in downward direction.

FIG. 110 shows as third possibility, an agitator blade which is driven by its own motor 525Compressed air may be introduced through a conduit 47, which compressed air will contribute to the equalization of the underpressure in groove 1.

FIG. 11d illustrates a design according to which the agitator blade 50 comprises an upper and lower disc 50a and 50b, each of which is adapted to create a special effect. The lower disc 50b is designed as a turbin wheel and is rotated by the supply of compressed air. The upper disc 50a is equipped with ribs or fins (not shown) and correspondingly creates a suction upon the turbid substance which is in the drop pipe 43 and descends from the trough 1.

The turbid substance is lifted by the under pressure prevailing in trough portion 1a through pipe 49 into said trough portion la.

The opening 41 in the partition between the trough portions 1 and 10 makes it possible whenever desired to eliminate the intermediate venting so that the turbid substance treated in the trough portion 1 may directly be conveyed into the trough portion 1a for further flotation.

lt is, of course, to be understood that the present invention is, by no means, limited to the particular show ing in the drawings, but also comprises any modifications within the scope of the appended claims.

Thus, mechanical or pneumatic devices for withdrawing the flotation turbid flow from the vacuum rangemay be omitted when the turbid substance is, in a manner known per se, subjected to a barometric drop which is sufflciently high to obtain the intended success.

What is claimed is: Y

1. In a vacuum foam flotation device: a housing, means for maintaining said housing at subatmospheric pressure, a trough in said housing and opening upwardly, means for supplying turbid liquid to said trough for flow therealong in said housing, foam pocket means in the housing laterally along at least one side of said trough, and foam stripper means movably mounted in said housing above said trough and movable therein in a direction to convey foam evacuated from above the turbid liquid in said trough to said foam pocket means.

2. A foam flotation device according to claim 1 in which said trough extends generally horizontally in said housing and said trough increases in depth in the direction of flow of turbid liquid therein.

3. A foam flotation device according to claim 1 in which said trough extends generally horizontally in said housing and said trough increases in width in the direction of flow of turbid liquid therein.

4. .A foam flotation device according to claim 1 which includes meansfor varying level of the turbid liquid flowin said trough.

5. A foam flotation device according to claim 4 in which said foam pocket means includes a plurality of individual foam pockets in side by side relation along said trough, division walls between adjacent ones of said foam pockets, and a discharge conduit leading from each said foampocket.

6. A foam flotation device according to claim 1 in which said means for supplying liquid to said trough comprises a supply nozzle which tapers to widen steadily outwardly in a direction toward width of said trough.

7. A foam flotation device according to claim 1 which includes means for supplying further air to said turbid liquid in a region spaced from the point of supply of the turbid liquid to said trough for augmenting the flotation process after the air entrained in the turbid liquid has passed off to such an extent that the flotation process is substantially diminished.

8. A foam flotation device according to claim 1 which includes means defining a flotation region under atmospheric pressure for receiving turbid liquid that has been subjected to suction in said trough.

9. A foam flotation device according to claim 1 in which the liquid flows in said trough in substantially laminar flow from the point of supply of the liquid to the trough, and means spaced from said point of supply for creating turbulence in the turbid liquid flow in downstream direction of the trough.

10. A foam flotation device according to claim 9 in which said means for creatingturbulence in said liquid comprises an impact screen isposed ending in spaced relationship transversely below the surface of the liquid in the trough and spaced along the trough from the point of supply of the liquid to the trough.

11. A foam flotation device according'to claim 9 in which said means for creating turbulence in the turbid liquid at a region spaced from the point of supply of the turbid liquid to said trough comprises fluid pervious outflow bodies below the level of the turbid liquid in said trough and adapted for passing fluid in either steady or pulsating flow to the liquid in the trough in a direction substantially transverse to the direction of flow of the fluid in the trough.

12. A foam flotation device according to claim 1 1 in which the fluid introduced through the fluid pervious outflow bodies is additional liquid that is saturated under overpressure with a gas.

13. A foam flotation device according to claim 12 in which said additional liquid introduced through said fluid pervious outflow bodies is admixed with flotation reagents for introduction transversely into the turbid liquid flowing in said trough.

14. A foam flotation device according to'claim 9 in which said means for creating turbulence in the turbid liquid flowing in said trough comprises a mechanical agitating mechanism spaced from liquid supply.

15. A foam flotation device according to claim 14 in which the bottom wall of said trough is provided with means forming a recess, said agitating mechanism being located within said recess, said agitating mechanism comprising blade means for driving liquid in the upward direction, and a quieting grate in said trough positioned above said agitating mechanism.

16. A foam flotation device according to claim 15 in which said trough includes a partition immediately upstream of said agitating mechanism having an opening near the lower end for the flow of turbid liquid to said agitating mechanism whereby the turbid liquid in said trough moves with laminar flow upstream of said partition and the agitation created by said agitating mechanism is confined to the region downstream of said partition.

17. A foam flotation device according to claim 16 which includes fluid supply means leading into said trough adjacent said agitating mechanism for the supply of fluid gaseously saturated under overpressure to the turbid liquid in the trough in the region thereof where the said agitating means creates turbulence in the liquid in said trough.

18. A foam flotation device according to claim 1 which includes means for bypassing turbid liquid from said trough at a point spaced from the point of supply of the turbid liquid thereto out of the subatmospheric pressure maintained within the housing and means for returning the thus bypassed turbid liquid back into a condition of subatmospheric pressure for continuation of the vacuum foam flotation process.

19. A foam flotation device according to claim 18 in which said means for bypassing turbid liquid includes a container open to the atmosphere for intermediately venting and adapted for receiving the said bypassed turbid liquid. 

1. In a vacuum foam flotation device: a housing, means for maintaining said housing at subatmospheric pressure, a trough in said housing and opening upwardly, means for supplying turbid liquid to said trough for flow therealong in said housing, foam pocket means in the housing laterally along at least one side of said trough, and foam stripper means movably mounted in said housing above said trough and movable therein in a direction to convey foam evacuated from above the turbid liquid in said trough to said foam pocket means.
 2. A foam flotation device according to claim 1 in which said trough extends generally horizontally in said housing and said trough increases in depth in the direction of flow of turbid liquid therein.
 3. A foam flotation device according to claim 1 in which said trough extends generally horizontally in said housing and said trough increases in width in the direction of flow of turbid liquid therein.
 4. A foam flotation device according to claim 1 which includes means for varying level of the turbid liquid flow in said trough.
 5. A foam flotation device according to claim 4 in which said foam pocket means includes a plurality of individual foam pockets in side by side relation along said trough, division walls between adjacent ones of said foam pockets, and a discharge conduit leading from each said foam pocket.
 6. A foam flotation device according to claim 1 in which said means for supplying liquid to said trough comprises a supply nozzle which tapers to widen steadily outwardly in a direction toward width of said trough.
 7. A foam flotation device according to claim 1 which includes means for supplying further air to said turbid liquid in a region spaced from the point of supply of the turbid liquid to said trough for augmenting the flotation process after the air entrained in the turbid liquid has passed off to such an extent that the flotation process is substantially diminished.
 8. A foam flotation device according to claim 1 which includes means defining a flotation region under atmospheric pressure for receiving turbid liquid that has been subjected to suction in said trough.
 9. A foam flotation device according to claim 1 in which the liquid flows in said trough in substantially laminar flow from the point of supply of the liquid to the trough, and means spaced from said point of supply for creating turbulence in the turbid liquid flow in downstream direction of the trough.
 10. A foam flotation device according to claim 9 in which said means for creating turbulence in said liquid comprises an impact screen disposed ending in spaced relationship transversely below the surface of the liquid in the trough and spaced along the trough from the point of supply of the liquid to the trough.
 11. A foam flotation device according to claim 9 in which said means for creating turbulence in the turbid liquid at a region spaced from the point of supply of the turbid liquid to said trough comprises fluid pervious outflow bodies below the level of the turbid liquid in said trough and adapted for passing fluid in either steady or pulsating flow to the liquid in the trough in a direction substantially transverse to the direction of flow of the fluid in the trough.
 12. A foam flotation device according to claim 11 in which the fluid introduced through the fluid pervious outflow bodies is additional liquid that is saturated under overpressure with a gas.
 13. A foam flotation device according to claim 12 in which said additional liquid introduced through said fluid pervious outflow bodies is admixed with flotation reagents for introduction transversely into the turbid liquid flowing in said trough.
 14. A foam flotation device according to claim 9 in which said means for creating turbulence in the turbid liquid flowing in said trough comprises a mechanical agitating mechanism spaced from liquid supply.
 15. A foam flotation device according to claim 14 in which the bottom wall of said trough is provided with means forming a recess, said agitating mechanism being located within said recess, said agitating mechanism comprising blade means for driving liquid in the upward direction, and a quieting grate in said trough positioned above said agitating mechanism.
 16. A foam flotation device according to claim 15 in which said trough includes a partition immediately upstream of said agitating mechanism having an opening near the lower end for the flow of turbid liquid to said agitating mechanism whereby the turbid liquid in said trough moves with laminar flow upstream of said partition and the agitation created by said agitating mechanism is confined to the region downstream of said partition.
 17. A foam flotation device according to claim 16 which includes fluid supply means leading into said trough adjacent said agitating mechanism for the supply of fluid gaseously saturated under overpressure to the turbid liquid in the trough in the region thereOf where the said agitating means creates turbulence in the liquid in said trough.
 18. A foam flotation device according to claim 1 which includes means for bypassing turbid liquid from said trough at a point spaced from the point of supply of the turbid liquid thereto out of the subatmospheric pressure maintained within the housing and means for returning the thus bypassed turbid liquid back into a condition of subatmospheric pressure for continuation of the vacuum foam flotation process.
 19. A foam flotation device according to claim 18 in which said means for bypassing turbid liquid includes a container open to the atmosphere for intermediately venting and adapted for receiving the said bypassed turbid liquid. 